Hedera helix (common ivy, English ivy, European ivy, or just ivy) is a species of flowering plant in the family Araliaceae, native to most of Europe and western Asia. A rampant, clinging evergreenvine, it is a familiar sight in gardens, waste spaces, on house walls, tree trunks and in wild areas across its native habitat. It is labeled as an invasive species in a number of areas where it has been introduced.

Hedera helix is an evergreen climbing plant, growing to 20–30 m (66–98 ft) high where suitable surfaces (trees, cliffs, walls) are available, and also growing as groundcover where there are no vertical surfaces. It climbs by means of aerial rootlets with matted pads which cling strongly to the substrate.

The leaves are alternate, 50–100 mm long, with a 15–20 mm petiole; they are of two types, with palmately five-lobed juvenile leaves on creeping and climbing stems, and unlobed cordate adult leaves on fertile flowering stems exposed to full sun, usually high in the crowns of trees or the top of rock faces.
The flowers are produced from late summer until late autumn, individually small, in 3–5 cm diameter umbels, greenish-yellow, and very rich in nectar, an important late autumn food source for bees and other insects.
The fruit are purple-black to orange-yellow berries 6–8 mm diameter, ripening in late winter,[4] and are an important food for many birds, though somewhat poisonous to humans.

There are one to five seeds in each berry, which are dispersed by birds eating the berries.[5][6][7]

The closely related species Hedera canariensis and Hedera hibernica are also often treated as subspecies of H. helix,[7][9] though they differ in chromosome number so do not hybridise readily.[6]H. helix can be best distinguished by the shape and colour of its leaf trichomes, usually smaller and slightly more deeply lobed leaves and somewhat less vigorous growth, though identification is often not easy.[7][10]

It ranges from Ireland northeast to southern Scandinavia, south to Portugal, and east to Ukraine and Iran and northern Turkey.
The northern and eastern limits are at about the −2°C winter isotherm, while to the west and southwest, it is replaced by other species of ivy.[5][6][7][8][9][11]

It is widely cultivated as an ornamental plant. Within its native range, the species is greatly valued for attracting wildlife. The flowers are visited by over 70 species of nectar-feeding insects, and the berries eaten by at least 16 species of birds. The foliage provides dense evergreen shelter, and is also browsed by deer.[5][12]

The species can become a nuisance in gardens, rapidly colonising hedges, trees and borders if not kept in check. It can even invade neglected lawns. Over 30 cultivars have been selected for such traits as yellow, white, variegated (e.g. 'Glacier'), and/or deeply lobed leaves (e.g. 'Sagittifolia'), purple stems, and slow, dwarfed growth.[13]

Like other exotic species, Ivy has predominantly been spread to areas by human action. H. helix is labeled as an invasive species in many parts of the United States, and its sale or import is banned in the state of Oregon.[28]

Laurus nobilis and Ilex aquifolium are widespread relicts of the laurisilva forests that originally covered much of the Mediterranean Basin when the climate of the region was more humid during the tertiary era. Having disappeared during the glaciation, Ivy is believed to have been spread back across the continent by birds once the continent warmed up again.[29] With a great capacity for adaptation, Ivy will grow wherever development conditions and habitat similar to that of its European origins exist, occurring as opportunistic species across a wide distribution with close vicariant relatives and few species, indicating recent speciation.

It is considered a noxious weed across southern, particularly south-eastern, Australia and local councils provide free information and limited services for removal. In some councils it is illegal to sell the plant. It is a weed in the Australian state of Victoria.[30]

In the United States, H. helix is considered weedy or invasive in a number of regions and is on the official noxious weed lists in Oregon and Washington.[32] Like other invasive vines such as kudzu, H. helix can grow to choke out other plants and create "ivy deserts". State- and county-sponsored efforts are encouraging the destruction of ivy in forests of the Pacific Northwest and the Southern United States.[33][34] Its sale or import is banned in Oregon.[35] Ivy can easily escape from cultivated gardens and invade nearby parks, forests and other natural areas. Ivy can climb into the canopy of trees in such density that the trees fall over from the weight,[34] a problem which does not normally occur in its native range.[5] For this reason, it is especially important to remove ivy from trees, creating "survival rings". In its mature form, dense ivy can destroy habitat for native wildlife and creates large sections of solid ivy where no other plants can develop.[34]

Ivy covering the walls of an old building is a familiar and often attractive sight. It may have insulating benefits, but can be problematic if not managed correctly. Ivy, and especially European ivy (H. helix) grows extremely rapidly and clings by means of fibrous roots which develop along the entire length of the stems. These are difficult to remove, leaving an unsightly "footprint" on walls, and possibly resulting in expensive resurfacing work. Additionally, ivy can quickly invade gutters and roofspaces, lifting tiles and causing blockages. It also harbours mice and other unwelcome creatures. The plants have to be cut off at the base, and the stumps dug out or killed to prevent regrowth.[36]